Sense 1slack -- (dust consisting of a mixture of small coal fragments and coal dust and dirt that sifts out when coal is passed over a sieve) => debris, dust, junk, rubble, detritus -- (the remains of something that has been destroyed or broken up)

Sense 3slack, slack water -- (a stretch of water without current or movement; "suddenly they were in a slack and the water was motionless") => stretch -- (a large and unbroken expanse or distance; "a stretch of highway"; "a stretch of clear water")

Sense 4mire, quagmire, quag, morass, slack -- (a soft wet area of low-lying land that sinks underfoot) => bog, peat bog -- (wet spongy ground of decomposing vegetation; has poorer drainage than a swamp; soil is unfit for cultivation but can be cut and dried and used for fuel)

Sense 5slack, slackness -- (the quality of being loose (not taut); "he hadn't counted on the slackness of the rope") => looseness, play -- (movement or space for movement; "there was too much play in the steering wheel")

Sense 6slack -- (a cord or rope or cable that is hanging loosely; "he took up the slack") => cord -- (a line made of twisted fibers or threads; "the bundle was tied with a cord")

Sense 7abate, let up, slack off, slack, die away -- (become less in amount or intensity; "The storm abated"; "The rain let up after a few hours") => decrease, diminish, lessen, fall -- (decrease in size, extent, or range; "The amount of homework decreased towards the end of the semester"; "The cabin pressure fell dramatically"; "her weight fell to under a hundred pounds"; "his voice fell to a whisper")